1. Field of Invention
This invention relates to apparatus and method for welding, and in particular to narrow groove welding using conventional welding equipment with a secondary gas cap which provides a large envelope of turbulent free cover gas over the weld puddle and which can be used to make complete deep narrow groove welds including the weld cap.
2. Background Information
Narrow groove welding is a term applied to welding in a v-shaped groove formed between the parts to be joined which has a "narrow" included angle. This technique is also referred to, especially in Europe, as narrow gap welding. While there is no precise definition of "narrow", welding with a groove having an included angle of less than about 50.degree. and certainly less than about 20.degree. is considered narrow groove welding. The obvious advantages of narrow groove welding are that less welding is required and it is therefore faster and uses less material. The implementation of the technique has not been totally satisfactory for field welding applications, however.
An important shortcoming of the implementations of narrow groove welding to date is that specialized equipment is required. A common arrangement for narrow groove welding utilizes a special elongated narrow gas cup referred to as a "chisel" cup. Typically, the torch block is customized to carry this chisel cup which surrounds the welding electrode and lays down an envelope of cover gas over the weld puddle. The envelope of cover gas delivered by this chisel cup is not very large and is vulnerable to drafts when outside the groove so that it is necessary to change the gas cup, and therefore, in some cases the torch block, to complete the weld cap. It also limits the operator's view of the weld puddle.
Another arrangement for narrow groove welding utilizes a specially designed circular, telescoping gas cup mounted on a customized torch block. After each several passes, the telescoping gas cup is incrementally retracted to accommodate reduction in penetration of the electrode into the groove. Typically these cups do not have sufficient cross sectional area to provide a large enough shielding envelope for welds deeper than approximately 3 inches.
There is a need for an improved apparatus and method for narrow groove welding.
There is a need for such an apparatus and method which can make deeper welds than presently possible with narrow groove welding equipment and which does not require a change in equipment to complete the weld cap and which improves the usability to the operator.
There is a further need for such a method and apparatus which can be utilized with conventional welding torches and consumables, both mechanized and manual.